In recent years, gas meters have various safety functions in order to secure proper and safe gas usage. In particular, such a gas meter is configured to shut off the gas when necessary by means of a shutoff valve included in the gas meter. To be specific, if a microcomputer included in the gas meter determines that the current state is abnormal based on a result of sensing by a flow sensor, seismic sensor, pressure sensor, gas leak alarm, or the like, then the gas is shut off by the shutoff valve (see Patent Literature 1, for example).
Shutoff valves using a PM stepping motor as a driving source, which are capable of realizing relatively strong closing force and returning force and capable of maintaining its state when non-energized, are attracting attention. In particular, a shutoff valve having an air-tight partition wall and including a rotor inside a gas passage and a stator outside the gas passage is attracting attention.
Some of the existing installed gas meters are not provided with such a shutoff valve as mentioned above. The necessity of installing a shutoff valve in such gas meters including no shutoff valve has been examined not only for safety purposes but also for the purpose of stopping gas supply to non-paying gas customers.    PTL 1: Japanese Laid-Open Patent Application Publication No. 2003-202259